1. Field of the Invention
The present invention relates to a crankshaft for a V-type six-cylinder engine.
2. Description of the Related Art
Generally speaking, a crankshaft used in a V-type six-cylinder engine is equipped with six crank pins, four crank journals, and nine arms for connecting the crank pins and the crank journals to each other. Some of these arms are each equipped with a counterweight for reducing the rotational force of inertia generated in each arm and the unbalance couple generated in the crankshaft.
In a conventional crankshaft, the counterweights are situated in a direction completely opposite the crank pins connected to the arms with respect to the central axis of the crankshaft. That is, in the case of an arm to which only one crank pin is connected, the counterweight is situated in a direction completely opposite that crank pin, and in the case of an arm to which two crank pins are connected, the counterweight is situated in a direction completely opposite the midpoint of the two crank pins.
An example of such a crankshaft is disclosed in JP 8-121539 A. According to the publication, the fourth arm and the sixth arm have no counterweights.
Conventional crankshafts have a problem in that the unbalance couple generated therein cannot be reduced to a sufficient degree.
This is due to the construction in which, in all the arms that are each provided with a counterweight, the respective centers of gravity of the counterweights are situated in a direction completely opposite the positions of the crank pins.